Retraction test using plug-in shape and script -

[Dantol 0]

How does Cura retraction plug-in test function? Viewing the g-code shows M117 which only writes to the display. No other retraction instructions are found. How is the retraction change?

No G1 E-d , where is retraction distance, G10, M207....

[GregValiant 1,409]

@Cuq is the author of the plugin and he can explain much better than I can.  I'll give it a shot because I'm awake.

 

If you have a G10 in the file you must have "Firmware Retraction" enabled in Cura.  Turn that off.  Cura changes it's own retraction settings according to the settings in the Post Processor.

 

If you haven't done so go to "Extensions / Post Processing / Modify Gcode" and then "Select Script".  One of the scripts is "Retract Tower".  The default is for Speed.  Below you can see that I've changed it to Distance.

 

The setting for Firmware Retraction is in the Printer Settings which must be loaded from the Cura Marketplace to make the settings accessible.

After you do your test (with Cura handling the retractions) you can set it back to Firmware Retraction if you like and the settings (Retract Distance, Retract and Prime Speeds) will get passed to the printer to handle with G10 and G11.  M207 contains the Retractions settings to be used by the firmware.

[Cuq 206]

https://github.com/5axes/Calibration-Shapes/wiki/Retract-Tower#note

[Dantol 0]

Thank you for your quick replies. I have done all that you have suggested, followed the Filament Friday video as well and read the write-up by Cuq.  I have retraction enabled and not using firmware retraction. I have switched to the retraction tower supplied by Teaching Tech Calculator in order to perform comparison prints.  I have adjusted my layer parameters for the Retract tower post script to accommodate the differences in  the tower that I am using.  The print using the gcode generated by slicing with Cura is not producing great results. Gcode supplied by the Teaching tech calculator produces a rather dramatic print with horrendous stringing with low retraction distance with observable improvement reaching 5mm for retraction distance. 

I have compared the gcodes in a text editor.  I can not find any command lines that would produce a retraction movement in the gcode produced with Cura (except at the beginning and end).  The other gcode have instructions  G1 E-d; where d = the retraction distance. 

Am I incorrect to assume that I would see some instructions in the gcode indicating a retraction move?

I am using Ender 3 and Anycubic Mega S printers.

[GregValiant 1,409]

For this example I'll use a retraction distance of 6.0mm.

If you are using "Relative Extrusion Mode" then there will be lines like

G1 X120 Y120 E0.45678    ;the last extrusion

G1 E-6 F2100                       ;Retraction

 

If you are using "Absolute Extrusion Mode" then they would look more like

G1 X120 Y120 E123.45678  ;the last extrusion

G1 E117.45678 F2100          ;Retraction

 

In relative mode the extruder always moves from "0" and so every retraction will be a negative number.

In absolute mode the extrusions are cumulative so the number keeps incrementing up and a retraction will be a subtraction.  Sometimes at the start of a print the number might be negative, but mostly you will see it as in my example where the "117.45678" is "retraction distance" less than the preceding line.

 

Generally, using "Relative Extrusion Mode" (it's in the Special Modes section of settings) can make a Gcode easier to decipher.

 

In Absolute Extrusion Mode you can search the gcode for "00 E" and you should come across the retraction and prime lines.

In Relative Extrusion Mode you would search for "E-" to get the retractions and "E5" to get the primes.

 

In Absolute Extrusion Mode Cura will reset the E number about every 10,000mm³ to avoid rounding errors that occur in the math.  For 1.75 diameter filament that's at about E=4158.  As the E value approaches that number Cura will add a G92 E0 to reset the extruder.

[Dantol 0]

thank you GregValiant!  I was assuming relative mode for the extruder.  Using the search code and Checking the previous E position proves out.  Now I wonder why my test prints using Cura are not as definitive as the prints using relative mode are.  I was using 6mm based on the Cura prints, but I could drop down to 4.5 - 5mm based on the relative mode prints.  

[GregValiant 1,409]

Whether you use Absolute or Relative (or Volumetric) the math and the numbers are the same and your prints should look the same.  A 6mm retraction is a 6mm retraction whether the extruder moves from "0 to -6", or from "3198.76543 to 3192.76543".

The math is always:

PIr² x Filament length = Volume of Filament going in

LayerHeight x LineWidth x ExtrusionLength = Volume of Filament going out.

When the ratio is 1:1 you have 100% flow.  (That is the reason why the exact filament diameter needs to be entered into Cura rather than just going by what the package says.)

 

What is the F number in those retraction lines in the relative file compared to what you have in the Cura file?

I can snap PLA back pretty fast but I've found that PETG doesn't like that.

 

[Dantol 0]

I totally follow you on your calculation .  As for the calibration prints looking different, I had done something funky with my start code in the past, but when I cleaned that up, the comparison prints started to look alike.  Thanks again.